Stabilized power actuator and method of operating same



May 9, 1950 E. D. LILJA 2,5@5,793

STABILIZED POWER ACTUATOR AND METHOD OF OPERATING SAME Filed Aug. 6, 1945 3 Sheets-Sheet 1 /].C.5DURU INVENTOR 4 Edgar D. Lilja BY 4 mflxk NE a ATT Y May 9, 1950 E. D. LILJA STABILIZED POWER ACTUATOR AND METHOD OF OPERATING SAME 5 heets-g 2 Filed Au 6, 1945 NVENTO Ed D L iU' BY gar M TORNF May 9, 1950 E. D. LILJA STABILIZED POWER ACTUATOR AND METHOD OF OPERATING SAME 3 Sheets-Sheet 5 Filed Aug. 6, 1943 Patented May 9, 1950 STABILIZED POWER ACTUATOR AND METHOD OF OPERATING SAME Edgar D. Lilia, Rockford, 111., assignor to Barber- Colman Company, Rockford, 111., a corporation of Illinois Application August 6, 1943, Serial No. 497,669

16 Claims. 1

The present invention pertains to power actuators or servos and method of operating the same. The general aim of the present invention is to provide a novel method and apparatus for effecting stabilization or anti-hunting action in such a device, and as a consequence of which a servo is able to follow with a high degree of accuracy the positional changes of a controlling element.

More particularly, it is an object of the present invention to provide a stabilizer arrangement for such an actuator or servo which operates through the use of automatic compensation for the effects of change in rate of movement of the servo in bringing the same accurately into a desired position.

Another object is to provide a servo in which the driven member is not only disconnected from its driver in bringing it to rest to free the member from the inertia effect of the driver, but in which such disconnection is effected at a control point which is varied automatically substantially in accordance with the rate and magnitude of change in speed of the driven member during its motion.

Still another object is to provide an arrangement affording a two-component potential for effecting the application of driving power to a driven member, one component persisting so long as the driven member is displaced from a predetermined point, and the other component, which is algebraically added to the first, being preponderately a function of the rate and magnitude of change in speed of the driven member.

A further object is to provide a servo or power actuator in which the application of power by the servo is proportioned in accordance with its displacement relative to a control member but with such applied power modified substantially in accord with changes in rate and magnitude of movement of the servo.

Still a further object is to provide a servo in which a change in speed is accompanied by a modification in an opposite sense of the applied power.

The invention also resides in certain novel features of the vacuum tube arrangement employed.

Further objects and advantages of the invention will become apparent as the following description proceeds, taken in connection with the accompanying drawings in which:

Figure 1 is a schematic view of a servo system provided with the improved power actuator and its control.

Fig. 2 is a fragmentary perspective view of one of the clutches included in the system of Fig. 1.

Fig. 3 is a perspective view of one of the clutch elements.

Fig. 4 is a fragmentary perspective view of a modified form of stabilizer unit adapted for use in the servo system of Fig. 1 in lieu of the stabilizer shown in the latter.

While the invention is susceptible of various modifications and alternative constructions, I have shown in the drawings and will herein describe in detail the preferred embodiment, but it is to be understood that I do not thereby intend to limit the invention to the specific form disclosed, but intend to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Reierring more particularly to the accompanying drawings, the invention has been shown in Fig. 1 as embodied in a servo or follow-up system in which a rotatable driven shaft l0 constitutes the driven member of a servo adapted for connection to any desired element (not shown) which is to be actuated. The shaft II] is arranged in the illustrated servo system to follow rotatively the motion of a rotary control shaft 1 1. Of course the control shaft l I may be turned by hand, the power, or in accordance with changes in any desired condition, whether mechanical, chemical or electrical. The point is that the control shaft H is shown as simply representative of any variable element whose successive conditions are to be reproduced in rotary motion by the driven member Iii. In the schematic showing of Fig. 1, a dial and pointer l2, I3 indicate the angular positions of the control shaft I I.

The illustrated servo comprises an electric motor [4 as a source of power for turning the driven shaft 18 upon connection thereto by alternately engageable friction clutches l5, 16 for respectively counterclockwise and clockwise rotation of the shaft I 0 (directions of rotation are designated with reference to a view of the shaft from its righthand end). The power transmitted from the motor I4 is governed by the degree of engagement or, to put it another way, by the amount of slip, in the selected one of the clutches i5, 16. These clutches have been shown as electromagnetically actuated and the amount of iorque transmitted thereby is substantially proportional to the energization of their actuating windings throughout their normal working range. It should be noted in passing that the principal purpose of utilizing a unidirectional motor with variably energizable friction clutches, rather than a variable speed reversing motor is to isolate the motor rotor mechanically from the driven shaft and its connected parts so that the inertia of the motor rotor will not aggravate the problem of stabilization. The clutches l5, lfimay take various forms, their construction per se forming no part of the present invention. The two are duplicates and suitable exemplary construction for the clutch is has been shown in Figs. 2 and 3. The driven element of the clutch comprises a thin disk 22 and covered in this instance. by a thin ring 22a of cork or other friction material. Radial slotting of the disk 22 minimizes warping. Hub 22b of the disk 22 is splined on a shaft that carries a gear 28 (see Fig. l) included-in the drive connection to the driven shaft ill, as hereinafter detailed. The shaft 25 is journaled intermediate its ends in a sleeve Zia which carries a gear 2! driven from motor pinion ill through a corresponding gear 26 of the other clutch It. The sleeve Zia carries the driving elements of the clutch, arranged on opposite sides of the driven disk 22. Such driving elements comprise a flange 23, a connected ring 24 of non-magnetic material, and an outer connected ring 26. Keys 25a secured to the ring 2% by screws 2511 project across the outer end of the disk into notches 21a, on the periphery of a plate 2i which is loose on the hub 22%) and is thus driven from the ring 25. Leaf springs 21b carried by the plate 2! act on the keys 26a to urge the plate 21 toward the ring 26 and thus maintain light mechanical contact at all times between opposite friction faces of the disk 22 and the ring and plate.

The rotating flange 23, 21 form part of a magnetic circuit through the plate 2?, which circuit is energized by a stationary electromagnet having a core l'ia on which the energizing winding ii is disposed between inner and outer poles Ito and lie with their faces located closely adjacent the flange-23 and the ring 26. The magnet core lid is provided with a mounting flange ild for stationary support of the same and the sleeve 2 la is journaled within such magnet core by suitable anti-friction bearings as shown. Energization of the winding ll tends to effect engagement of the mating clutch elements, the amount of torque transmitted between the latter being a function of the energization of the winding. As the energizing current for the winding ii is increased the torque supplied by driven shaft 25 increases and vice versa.

Gears 28, 25 on the driven shafts of the clutches [5, IE mesh with a gear 3t, common to the two, and accordingly the direction of rotation of the shaft 3| for this gear 39 is dependent upon which of the two clutches is engaged. From the shaft 3| to the shaft is the drive is by way of a suitable gear train 32. The latter includes a pinion 32a on the shaft 3| meshing with the gear 321) of a gear and pinion cluster 32b, 320, the pinion 320 of the latter meshing with a gear 32d fast on the shaft E0.

The novel stabilizing arrangement herein contemplated has been illustrated as embodied in the servo whose general construction has been outlined above. Before describing the novel stabilizer arrangement, however, a brief identification will be made of other elements of the particular servo system in which the invention is exemplifled. As to such system, the angular positions of the shafts ill and I l are compared through the use of a transmitter synchro 33 and a transformer synchro 34. These devices each have a stator and a rotor, the rotors being connected respectively to the shafts H and HJ. Such synchros,

the ring 26 and the platesometimes known respectively as synchronous transmitters or synchronous transformers, are well-known commercial products and operate in a manner well understood for such devices, so that detailing here is unnecessary. In brief, the transmitter synchro 33 is provided with a primary winding on its rotor and an inductively coupled three-phase secondary winding 36 on its stator. The primary winding 35 is excited from an alternating current supply line 3?. The terminals of the stator winding 36 of the transmitter 33 are connected to the corresponding terminals of three-phase stator windings 38 of the transformer synchro 34. The latter windings are inductively coupled with a single phase winding 39 on its rotor.

When the synchros are connected in the manner set forth above a voltage is induced in the winding 39 or the transformer synchro which is a sinusoidal function of the discrepancy between the angular positions of the synchro rotors, or, in other words, the shafts it and I I. When the two shafts occupy the same angular position, the induced voltage in the winding 39 is zero, but when the position of the shaft iii lags or leads the position of the shaft ii, a voltage is induced in the winding and the phase of this induced voltage reverses with respect to that of the line 37 when the direction of such discrepancy is changed. In general, then, a potential is produced in the winding 39 which persists throughout any discrepancy in position between the shafts it and H, which is proportional in magnitude to such discrepancy, and which is of a sense corresponding to the sense of such discrepancy. By the term sense of a potential, as used herein, is meant the direction of a direct current or, correspondingly, the phase of an alternating current with respect to some reference phase such as that of the alternating supply for the system. In the present instance it happens that alternating current is employed.

The potential induced in the winding 39 of the transformer synchro 34 is, together with a second potential provided for stabilizing purposes in a manner hereinafter described, applied to the input circuit of the first stage amplifier tube 48 of a multi-stage amplifier and electronic control network. The output stage of this network is utilized in effecting selective energization of the clutches i5, it as hereinafter detailed. In considering the network, it will be observed that in the input of the first stage tube i. e., between its cathode 4| and control grid 42, two bridges 43 and 44 are connected in series. These bridges each constitute a phase shifting means of wellknown form comprising resistances and capacitances connected in opposite legs of each bridge. Input terminals 4%? of the bridge are supplied through conductors at with the potential induced in the transformer synchros winding 3:), while the input terminals 4T of the other bridge 4d have a second potential impressed thereon through conductors 48 for stabilizingpurposes, as hereinafter set forth. To connect the outputs of the bridges 43, 44 in series in the input circuit of the tube 46, one output terminal 49 of the bridge 43 is connected to the cathode 4i through a conductor 5i) and resistor 55 shunted by a condenser 52., while the other output terminal lsa of this bridge is connected by conductor 55 to output terminal 54 of the other bridge 44. The other output terminal 54a of the latter bridge is connected to the grid 42 through a resistor 55.

The amplifier network may, of course, take a ing [8 of clutch it.

variety of forms. In the particular layout shown the first stage tube 463 is a pentode, having, in addition to the elements already noted, a screen grid 56, a suppressor $57 and an anode 58. In the output circuit of this tube it plate voltage is supplied from a battery 59, which is connected betweenthe cathode and anode in series with a load resistor 66 and biasing resistor 5| shunted by condenser 52.

The second stage of the amplifier comprises a triode (all having a cathode 62, a control grid 63 and an anode fi l. The control grid 63 is coupled to the output of the first stage tube 40 through a condenser 55 and the input circuit of the tube 65 is completed from the grid 53 to the cathode 62 through resistors 6t and 6'1, the latter being shunted by a condenser 68. The primary winding 69 of a coupling transformer is connected in the output circuit of the tube 6|, plate voltage being also supplied for this tube from the battery 59.

The final or output stage of the network comprises four tubes ll, i2, i3 and it. The tubes 1 l, T2 are arranged to control the clutch it, While the other two tubes it, it are arranged to control the clutch it. Each of these tubes is shown as a triode, having respective cathodes l5, l6, l1, l8, respective grids re, 89, 8E, 82, and respective anodes 83, dd, E35, On the input sides of the tubes ii to it their grids are connected to a secondary winding sea of the coupling transformer 10. Thus, the grids of tubes ll and it are connected to one end terminal of this winding, while the grids of tubes i2 and i3 are connected to the other end terminal of this winding, its center terminal being connected to the common line 59. On the output sides of the tubes ii to T4 plate voltage is supplied from two power transformers Bl and 88 having respective primary windings 89 and 90 excited from the alternating current supply lines 3?. These transformers are provided with secondary windings 9i and 92 respectively, having center taps connected to corresponding ones of the clutch exciting windings l8 and I! through conductors 93 and 94. Such exciting windings have a common return line 95 to the cathodes of the four tubes ll to it. The end terminals of the transformer secondary winding 9| are connected to the respective anodes of tubes H and 12, while the end terminals of the other transformer secondary winding 92 are connected to the anodes of the other two tubes 13 and 14.

Of the four tubes ii to 14, only one is conductive at any one time. The one of these tubes which is at any given instant conductive is that one whose grid is connected to what is at that instant the positive side of the transformer secondary winding 69a and whose plate is at that instant energized positively from the corresponding one of the transformers 81, 88. By way of illustration, it may be assumed that at a given instant the righthand terminals of each of the three transformer secondaries 39a, 9| and 92 are positive and the lefthand terminals negative. In such case only the tube l I has the necessary combination of positive plate potential and relatively positive grid potential to render the tube conductive, wherefore current flows through its plate circuit energizing the winding I8 of the clutch it. On the next half cycle all of the polarities will be reversed and the companion tube '42 will conduct, again energizing the wind- If, however, the phase of the voltage across the transformersecondary winding 69a is reversed, as is the case when there" is a discrepancy in angular position between the shafts l0 and H in a sense opposite to that prevailing for the conditions assumed above, the other two tubes 73 and 14 will conduct during alternate half cycles, thereby energizing the winding I? of the clutch l5. It is to be observed that the grids of the tubes l! to M are not permitted to become positive with respect to their corresponding cathodes by virtue of the negative biasing applied to such grids with respect to their cathodes. The negative bias is effected by means of a voltage divider comprising resistors 96, 91 connected across the battery 59 by a conductor 98 and having a mid tap connected by a conductor 99 to the common line of the cathodes.

From the foregoing it will be seen that since the conduction of the tubes 1! to M is dependent on the phase relation of the voltages on their input and output circuits, it is requisite that the phase of the voltage induced in the transformer secondary winding agree closely with that of the voltage in the lines 3?. It is in order to facilitate the adjustment of this phase relation that the phase changing bridges 43 and 44 are provided. Through adjustment of the same in their well-known manner, the required phase relation of the voltages noted may be readily obtained in setting up the system.

As so far described, the circuit is such that any discrepancy in position between the driven shaft if: and transmitter shaft it causes the appropriate one of the clutches i5, is to be engaged for turning the shaft if! in a direction to restore it to coincidence in angular position with the control shaft H, such energization of the proper clutch persisting until the shaft it has turned to the position predetermined by the location of the shaft H. In the absence of other provision, however, this operation would be accompanied by considerable hunting with consequent loss in accuracy of the positioning of the shaft ID relative to the control shaft H. In accordance with the present invention the arrangement next to he described has been provided for stabilizing the action of the system in order to obviate such hunting and enhance the accuracy of the control.

In brief, stabilization is effected by terminating the energizing voltag of the engaged one of the clutches i5, 55 at a point automatically determined as a direct function of the relative velocity between the rotor i 62 and stator till. Such point of termination of the voltage applied to the engaged one of the clutches, or, in other words, termination of the application of driving power to the driven member, may be conveniently designated as the control point, and the presently disclosed stabilizer is adapted to effect a shift of that control point. During acceleration of the driven member, the cont ol point is reached earlier by reason of the stabilizer action, and during deceleration the control point is postponed. Expressed in terms of rotation, when the shaft i0 is rotating clockwise and is accelerating, the control point is shifted counterclockwise and is reached sooner than otherwise. On the other hand, if the shaft it is running clockwise and is decelerating, the control point is advanced in a clockwise direction and is reached later by reason of such shift.

In the present instance such shift in the control point is effected by adding algebraically to the input potential of the amplifier network previously described and derived from the phase amines ''hi-l ten ii'ridge dil, a second component ofpatch.-

simpressed on the circuitsby way of .lphase-shi'fter bridge ii. This second potentialdsof' a sense. opposite to such ra e of eliange; that is, if the shaft is is. accelerating, the potential: supplied from bridge to is opposite in'sense to the. potential from bridge it, while ittheishafit. l e. is decelerating the potential from bridge TM is of the same sense...as that from the bfld'gei li. To put it another way, when the transmitter and shaft are accelerating the 130.- iientialsare opposed and when the shaft is decelerating they are additive, In both instances theirnagnitnde of the second potential compo nentiis a complox function of the rate and magnitudeziof change of speed of the shaft The :netrresult, achieved in the exemplary system by suoh al ge'braic addition of the two potential components noted, is to provide an energizing potential for the clutches 5, it which is terminated at anoint varied automatically in accordance with the magnitude and time duration of acceloration or deceleration of the shaft it.

'lTheiadditional or second potentialgnotedabove being provided for stabilizing purposes, is in theillustrated apparatus supplied from an induction generator I09 having a shell type stator is! and a squirrel cage rotor M2, the latter being fixed to the shaft 3i. n the four pole pieces of the stator it! :is a diametrioally'opposed pair of windings I03 energized from the alternating current supply lines 3? through conductors its and slip rings 35, as well as a second diametrically opposed pair of windings Hi6 connected to the bridge tl i'through conductors t3 and slip rings +061. Whenth rotor it? turns in relation to "the-stator Hill a voltage is induced in the, windings 1&6 which is proportional to the speed of the rotor relative to the stator. Stated in other words, the voltage induced in the windings H35 ispr'oportional 'to the discrepancy in speed between the driven shaft 3i and the stator 552i. :Suchproportionality of output voltage to speed is characteristic of induction generators.

.In the stabilizer setup illustrated in Fig. 1, both :t'he'rotorandstator of the generator Hill are revoluble, one being turned at a speed varying precisely wthat that of the shaft !0 and the other ibeing driven by a magnetic drag coupling between l [I and we tends'to turn at the same speed "as the shaft !!32. Accordingly, the differential, wh'en any exists, in speed between the two generator elements (and which results in an output "voltage of proportional magnitude) is a complex' funct-ion of the rate of changes in speed of Lie the-sha-ft ii]. In the present instance the rotor is-'fiited directly to the shaft 3i so that its speed corresponds exactly to the instantaneous speed "of the shaft Ill, the actual ratio of the rotor speed #:othat of shaft l0 being determined by the ratio er the-gearing between them. The stator NH is, on the other hand, as a result of the combined action of the inertia of stator It! and the slip connection, revolved at a speed which changes "relatively less rapidly than that of shaft l8, and will ultimately, for constant speeds of said shaft, -'-rotate at'approximately the same speed as the In the apparatus shown in Fig. 1 the stator is itself adapted to act as an inertia "member or flywheel in accomplishing its rotation at the desired average speed. The stator, because of its inertia and the fact that it is driven thy-ca slipping connection from the rotor, rotates 'at-a less rapidly varying speed determinedby:

$he stabilizer constants, the speed of the rotor,

and: the variations rotorespeed duringsa short timeinteryalspreceding the instant lander consideration lluringperiodsiofuconstantaccele oration oi.- deceleration of the rotor, there. tendsJ therefore, .to be. :a speed difierencel between the -mtorlandstator.

Torque is :applied to the. generator stator @l 6 I for dinning it from: theshaft. 31 through what may be termed a slip connection in. order: that the relatively larg-e inertia stator, acting-as. it does as a tlywhe'el, may revolve at a relatively constantspeed: but may, nevertheless, tunncle. tiveto the rotor -14] 2 on the-latter when occasion demands. coupling is located-between-the shaft Manda stator supporting frame I88, the latter-being carried by a-shaft108a, revoluble oo- "axially-wi'ththeshaft 31. Theron-191mg oomprisesadisk type of drag device including-an electrically conductive, non-magnetic disk- 18!! ma'deef copper or --aluminum and fixed "to the shaft 3|. This disk is interposed-between-arrannular series of -'-U--shaped--permanent magnets l I 0 and-soft iron keeper ring I H, both fixed to-the fraine lil8--coairially with the shaft 408a. 'Ehe fiux created-by the permanent magnets I-H'l 'threads fr'om one leg of each through the disk into the keeper HI and thence back through the disk into the other leg of "each such magnet, and infso doingsets up eddy currents in the disk we; 'e rerting atorque on the "diskwhich is pro;- portional to its speed relative "to the permanent magnet, In consequence 'ofthis connection, the '"torquerexerted on the stator is "directly proportioned-"to the differential in speed between the and rotor.

way'of 'recapitulation of the operation'of the: disclosed system described above, it willbe noted that-a potential is supplied from thesyrrchro winding "39 which is "of a sense and of' a magnitude proportional" to any deviation in position of the shaft-10 with reference to shaft 11. Acting alone, this potential, opera-ting throng-h the vacuum "tube net-work described,*caiises energ izationof the appropriateoneof the clutches 115;, l-ii to revolve theshaft [0 into angular coincide'noe with the-shaft H. Moreover, thedegree of energization of' the "one of I the-clutohesren dered-operative- 'is generally proportional to-the ai'nount ofdiscrepancy in shaft position. The clutch slippage -is-thus proportionately decreased asthe discrepanoy-may be increased so that'the greater-the displacement-of the shaft lfl'with ref erenc'e to the control shaft 11, the grea-tei will be *thetorque exerted. By way of' stabilization,

however, to avoid-hunting and-inaccuracy =0:

servo positioning; theaction just-described, is -in accordance the present invention, modified.

Such modification-consists;of a change in the poteritial supplied to the amplifier network, in the present i-nsta-nce through the imposition -of a second potential component which is preponderately'a' iunction of the rate andmagnitu'deof cl 1ange in-speed-ofthedriven shaft I U'. Thu-s in the event 'of acoeleration of the shaft I 9 a potential is produced-in thegenerator windings I anceout to zero, i. e -the controlpoint at wh'ich "theapplicationofpower -to the shaft i0 is interrupted by the opening of the one of the clutches which has been closed, is reached sooner in point of time by an amount which is a function of the acceleration and change in velocity. Conversely, if there is a deceleration of the shaft II] a potential is again produced in the generator windings I06 of a magnitude which is a function of the rate and magnitude of such change in speed, but in this case is impressed n the amplifier network in voltage addition to the potential derived from the transformer synchro 34. Consequently, the control point is in such case advanced in the direction of rotation of the driven shaft I a.

Not only is the control point shifted as described but, in addition, a corresponding change is worked in the speed of the shaft ID in approaching its zero discrepancy position. In particular, during acceleration of the shaft II! the power transmitted to it is diminished by the increase in clutch slippage resulting from the decrease in applied current occasioned by the control potential derived from the generator I09. Conversely, during deceleration of the shaft ID, the power transmitted to the shaft I0 is increased, through decrease in clutch slippage brought about by the increase in applied current occasioned by the control potential from the generator I00.

In Fig. 4 is shown a modified form of stabilizer adapted for incorporation in the system of Fig. 1. In Fig. 4 the shaft 3| corresponds to the shaft 3i of Fig. 1 and the generator IIIQ' corresponds to the generator IUD, serving as the latter did to produce the desired potential for stabilizing purposes.

In the unit of Fig. 4 the establishment of generator connections is simplified, that is, the necessity for slip rings or the like is eliminated, by utilizing an arrangementin which the generator stator IBI' is stationary, being mounted on a frame II2. To accommodate such revision, the flywheel function performed in Fig. 1 by the revoluble stator is efiected in this case by a sepa rate inertia member or flywheel I I3. The desired differential in speed between the speed of this inertia member and the instantaneous speed of the shaft 3| is imparted to the generator rotor I 02' through the use of a differential gearing designated generally as H4. Basically the setup is the same as that of Fig. 1 in that the arrangement is such as to cause the generator IUD to produce a control potential which is substantially proportional in magnitude to a function of both the acceleration and magnitude of change in speed of the load and of a sense, relative to the potential produced by the associated synchros, which, for simultaneous movement of said synchros in the same direction, is inverse to the sense of the rate of change in speed of the servo. The control potential so produced may be applied in the general system in the same manner as illustrated in Fig. l and the overall operation of the system is the same.

Turning now to the details of the stabilizer shown inFig. i, the shaft 3! carries a gear II5 meshing with a gear H6. The latter is fixed to a sleeve II'I coaxial with a shaft H8, but journaled for free rotation relative to the latter on antifriction bearings H9. Also rigid with the sleeve II! is the intermediate I22 of the differ ential gearing I I4.

The diiferential gearing II4 comprises, in addition to the intermediate I 2%], first and second terminal elements or gears I2I, I22 arranged sideby-side coaxially with the shaft IIB, as well as planet pinions I23, I24 journaled on the intermediate I20 for bodily rotation therewith and meshing respectively with the first and second terminal gears, as well as with each other. The first terminal gear I2I is connected to the flywheel I I3, both of these elements being pinned to the shaft I I 8. The other terminal gear I22 is, on the other hand, pinned to the shaft I25 of the generator rotor I02.

The generator I00 operates as an induction generator and is shown as being constructed in a form ordinarily employed for shaded pole motors. Thus its stator IOI is of the core type and has on it a main energizing winding I03, energized from a main alternating current supply line, as well as auxiliary windings I 06 linked by the flux passing between the stator and the squirrel cage rotor I02. Upon turning of the rotor I02 a potential is thus induced in the windings I06 which is proportional in magnitude to the speed of the rotor relative to the stator and of a sense dependent upon the direction of rotation.

A magnetic drag device designated generally as I25 is applied to the generator rotor I02. In this instance the drag device consists of a cup I2? made of non-magn tic electrically conductive material, such as copper or aluminum, pinned to a shaft I28 which is in turn rigidly connected to the rotor shaft I 25. The cup I 21 is received between the opposed annularly disposed pairs of pole pieces I22, I 35! of a stationary permanent magnet I3I. As a consequence of the eddy currents set up in the cup I2! by the flux from the permanent magnet, a torque is exerted on the generator rotor I92 which is proportional to the speed of rotation of. the same. Since the restraint offered by this magnetic drag device is zero at zero speed by the motor, and very small at low speeds, it is sometimes necessary to supplement it by a small friction drag (not shown) applied to the shaft I28 to prevent the generator rotor I02 from rotating during constant speed conditions for the servo.

In considering the operation of the apparatus shown in Fig. 4, it may first of all be assumed that the shaft SI is revolving at constant speed. In such case the intermediate I22 of the dinerential gearing I! is also revolved at constant speed, as is the first terminal gear IZI and the flywheel H3. The second terminal gear I22, as well as the connected generator rotor H32, remains stationary. wherefore no potential is produced in the generator Hi In the event that the shaft 3! accelerates or decelerates, however, from such constant speed, the speed of the intermediate I22 changes. The flywheel H3, acting on the first terminal gear $2I, resists a corresponding change in speed of the latter, wherefore the second terminal gear I 22 forced to turn, thus revolving the generator rotor 692. It is clear that the generator rotor will tend to revolve in one direction for acceleration of the shaft 3I and in the opposite direction for deceleration and that, moreover. the speed of the generator rotor will be preponderately a function of the rate of acceleration or de eleration and amount of change in speed of the shaft 3 I. Ac cordingly, a control potential of the desired magnitude and sense is provided for modifying the control potential derived from the synchrcs of Fig. l in the manner heretofore described for stabilization purposes.

I claim as my invention:

1. The combination with a rotary driven member and an electrically controlled actuator therefor operable to revolve the driven member at a speed corresponding to the degree of energ-izati'on of the actuator, of a revoluble-inertia "member, coupling means tending to revolve the inertia member from said actuator at the speed of sai'd driven member, and means for modifying the energization of said actuator in accordance with departures in the rotative speed of said driven member relative to that of said inertia member.

2. In a stabilizer fora rotary driven member, the combination of a revoluble inertia member, means tending to revolve the inertia memher at the speed of the driven member, and means for producing apotential of a sense corresponding to any departure in rotative speed of the driven element relative to that of said inertia, member and proportional in magnitude to such departure. V

3. The combination with arotary driven memher and an electrically controlled actuator there for operable to 'aprpiy to the driven member a torque corresponding to the degree of energization of said actuator, of a revoluble inertia member, a coupling for applying a torque to said inertia member substantially proportional to the relativespeed-of rotation between the same and said amen member, and means for modifying the responding to the degree of energization of said actuator, means for supplying a first control potential corresponding in sense and magnitude 'to any discrepancy in position between said driven member and a'control member therefor, a revoluble inertia member, coupling means for connecting said inertia member in driven relation with said actuator to revolve at a speed at or approaching that of said driven member, means for supplying a second control potential pr portional in magnitude to any departure in the speed of said driven -member relative to that of said inertia member and of a sense, relative to that of the first potential, corresponding inversely to the sense of such departure, and means for energizing said actuator in accordance with the algebraic sum of said potentials.

, :5. The combination of a rotary driven member;.-ian electrically controlled actuator therefor operable to revolve the driven member with a torque corresponding to the degree of energization of said actuator, means for supplying afirst potential corresponding in sense and magnitude to any discrepancy in position between said driven member and a control member therefor, an induction generator having independently revoluble rotor and stator elements, means for revolving one of said generator elements in unison with said driven member, means for revolving the other generator element in the same direction as the first at a speed at or approaching that of said driven member, the relative motion between said. generator elements occasioned by change in rate of speed of said driven member resulting in the generation of a second potential proportional in. magnitude and sense to such change, and means for energizing said actuator in accordance with the algebraic sum of said first and second potentials.

6. The combination of a rotarydriven member and an electrically controlled actuator therefor, an induction generator having independently revoluble rotor and stator elements, means for'drivi2 ing said rotor element from said actuatorflin unison withsaid driven member, a coupling'for transmitting a torque from said actuator to said stator element substantially in proportion to the relativespeed of said generator elements, the'inertia of said stator tending to cause the samc to revolve at a speed more uniform than that of the rotor but which is always approaching the speed of the rotor, and means for utilizing the potential produced by said generator to modify the power applied by said actuator to said driven member.

'7. The combination of a rotary driven member, an electricallycontrolled actuator therefor, agenerator having rotor and stator elements, a revoluble'inerti'a member, a difierential gear including first and second terminal elements and an intermediate element, means for revolving said intermediate element in unison with said driven member, means connecting said first terminal element to said inertia member and the second terminal element to one of said genena'tor elements, means for applying a torque to said secondelement resisting the turning thereof substantially proportionately to its speed of movement, anyrdeparture of the intermediateelement from the corresponding average speed established by said inertia member resulting in a turning of said rotor and consequent production of potentialb-y said generator, and means for utilizing the potential produced by saidgenerator to modify the power applied by said actuator to said driven member.

'8. In a servo system the combination comprising a driven member subject to changes-in speed; a reversible power means for moving'the'driven member; and stabilizer means, said stabilizer means including means responsive to the speed of said driven. member which prevails immediately prior to a change in speed thereof, means responsive to thecspeed of said driven member which prevails immediately subsequent to a change in speed thereofla slip connection includingia drag'device for drivingly coupling together said speed responsive means, and means actuated conjointly by said speedresponsive means for varying the application of power to the driven member.

9. In a servo system the combination comprising a driven member subject to changes in speed; a reversible power means for moving the driven member; and stabilizer means, said stabilizer i'neansincluding a first rotatable member rotating accordance'vzith the speed of said driven memher which prevails immediately prior to a change in speed thereof, a second rotatable member rotating in accordance with the speed of said-driven member which prevails immediately subsequent to a change in speed thereof, means having substantially the speed-townie characteristics of an eddy current drag coupling for gradually reducing the discrepancy in speed between said rotatable members resulting from said speed change, and means energized in response to the discrepancy in speed between saidrotatablemembers for varying the application of power to the driven member.

10. Ina servo system the combination c0rnprismg a rotary'driven member, an electrically controlled actuator therefor, a rotary control member, means for supplying a first control potential correspondingin sense and magnitude to any discrepancy in position between said driven member and said control member, meansresponsive to the speed of said driven member immediately prior to a change ofspeed thereof, means responsive to the speed of said driven member immediately subsequent to a change of speed thereof, and means actuated conjointly by said speed responsive means for deriving a stabilizing control potential which is a function of the magnitude of said change of speed, and means for energizing said actuator in accordance with the algebraic sum of said potentials.

11. In a servo system the combination comprising a rotary driven member, an electrically controlled actuator therefor, a rotary control member, means for supplying a first control potential corresponding in sense and magnitude to any discrepancy in position between said driven member and said control member, means responsive to the speed of said driven member immediately prior to a change of speed thereof, means responsive to the speed of said driven member immediately subsequent to a change of speed thereof, and means actuated by said speed responsive means conjointly for deriving a stabilizing control potential which is a function of the magnitude of said change of speed and of a sense opposite to the sense of said change of speed, and means for energizing said actuator in accordance with the algebraic sum of said potentials.

12. The method of effecting stabilized operation of a servo which comprises producing a first potential corresponding in magnitude and sense to the discrepancy in position of the servo relative to the associated control member therefor, driving a rotatable inertia member at a speed which corresponds to the speed of said servo upon constant rotation thereof but which resiliently lags the speed of said servo upon increasing the speed thereof by an amount which is a function of the rate and magnitude of the speed change, generating a second potential of a magnitude proportional to the difference in velocity of said servo and said inertia member and negative in sense with respect to said first potential, algebraically combining said potentials into a resultant potential, and applying power to said servo in accordance with said resultant.

13. In a servo system having a transmitter, the combination comprising a driven member, a drive motor, an electromagnetically engaged clutch interconnecting said driven member and said drive motor and having a torque transmitting characteristic substantially proportional to the electrical energization thereof, means for deriving a first control potential in accordance with the angular displacement of said driven member with reference to said transmitter, means for deriving a second control potential only upon changes in the speed of rotation of the driven member and in an amount which is a function of the difierence between the rotative speed of said driven member immediately prior to a change of speed as compared to the speed immediately subsequent to such change, and means for modifying the energization of such clutch in accordance with the algebraic sum of said control potentials.

14. In a servo system the combination comprising a driven member subject to changes in speed; a reversible power means for moving the driven member; and stabilizer means, said stabilizer means including a rotatable member rotating in accordance with the speed of said driven member, a flywheel, an eddy current drag coupling for coupling said rotatable member and said flywheel and for gradually reducing the discrepancy in speed therebetween resulting from said speed change, and means energized in response to the discrepancy in speed between said rotatable member and said flywheel for varying the application of power to the driven member.

15. In a servo system the combination comprising a rotary driven member, an electrically controlled actuator therefor, a rotary control member, means for supplying a first control potential corresponding in sense and magnitude to any discrepancy in position between said driven member and said control member, means responsive to the speed of said driven member immediately prior to a change in speed thereof, means responsive to the speed of said driven member immediately subsequent to a change in speed thereof, and means actuated conjointly by said speed responsive means for deriving a stabilizing control potential which is a function of both the magnitude of said change of speed and the rate at which such change occurs, and means for energizing said actuator in accordance with the algebraic sum of said potentials.

16. In a servo system the combination comprising a rotary driven member, an electrically controlled actuator therefor, a rotary control member, means for supplying a first control potential corresponding in sense and magnitude to any discrepancy in position between said driven member and said control member, means responsive to the speed of said driven member immediately prior to a change in speed thereof means responsive to the speed of said driven member immediately subsequent to a change in speed thereof, and means actuated by said speed responsive means jointly for deriving a stabilizing control potential which is a function of the magnitude and rate of said change of speed and of a sense opposite to the sense of said change of speed, and means for energizing said actuator in accordance with the algebraic sum of said potentials.

EDGAR D. LILJA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,115,086 Riggs Apr. 26, 1938 2,176,102 Riggs Oct. 17, 1939 2,403,605 Lesniek July 9, 1946 FOREIGN PATENTS Number Country Date 489,271 Great Britain June 20, 1936 

